Amino acid residues important for D-galactose recognition by the F-type lectin, Ranaspumin-4

Area of Science:

• Biochemistry
• Molecular Biology
• Glycobiology

Background:

• F-type lectins typically bind L-fucose and possess conserved binding motifs.
• Ranaspumin-4, an F-type lectin from the Tungara frog, is an exception, showing D-galactose specificity.
• Despite sequence similarity to other F-type lectins, Ranaspumin-4 does not bind L-fucose.

Purpose of the Study:

• To elucidate the detailed glycan-binding profile of wild-type Ranaspumin-4.
• To identify specific amino acid residues responsible for D-galactose recognition in Ranaspumin-4.
• To understand the structural basis for Ranaspumin-4's unusual lectin specificity.

Main Methods:

• Hemagglutination inhibition assays
• Flow cytometry assays
• Enzyme-linked lectin assays
• Rational site-directed mutagenesis

Main Results:

• Ranaspumin-4 exhibits specific binding to terminal D-galactose residues.
• The lectin shows a preference for α1-3, α1-4, β1-3, and β1-4 D-galactose linkages.
• Methionine at position 31 (M31), replacing a conserved glutamine, is critical for D-galactose recognition.
• Residues Q42 and F156 also appear to contribute to D-galactose binding.

Conclusions:

• Ranaspumin-4 possesses a unique D-galactose binding specificity within the F-type lectin family.
• Specific amino acid substitutions, particularly M31, are responsible for this altered binding preference.
• The study provides insights into the structural determinants of lectin specificity.